A dc-DC converter includes a substrate having opposing first and second sides, a power stage attached to the first side of the substrate and having active semiconductor components operable to provide an output phase of the dc-DC converter, an inductor attached to the first side of the substrate and electrically connected to the power stage through a first metal trace at the first side of the substrate, and a plurality of electrically conductive vias extending through the substrate from the first side to the second side. The vias are electrically connected to the first metal trace. At least some of the vias are disposed at least partly under the power stage. A corresponding method of assembling such a dc-DC converter also is disclosed.
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1. A dc-DC converter, comprising:
a substrate having opposing first and second sides;
a power stage attached to the first side of the substrate, the power stage comprising active semiconductor components operable to provide an output phase of the dc-DC converter;
a discrete inductor individually separate and distinct from the substrate and the power stage, the discrete inductor attached to the first side of the substrate and electrically connected to the power stage through a first metal region at the first side of the substrate; and
a plurality of electrically conductive vias extending through the substrate from the first side to the second side,
wherein the vias are electrically connected to the first metal region,
wherein at least some of the vias are disposed at least partly under the power stage,
wherein a first terminal of the discrete inductor is attached to the first metal region,
wherein a first group of the vias is disposed along a first side of the first terminal and a second group of the vias is disposed along a second side of the first terminal opposite the first side of the first terminal,
wherein a second terminal of the discrete inductor is attached to an output voltage metal region at the first side of the substrate,
wherein the output voltage metal region is spaced apart and electrically isolated from the first metal region,
wherein a first plurality of additional vias is disposed along a first side of the second terminal,
wherein a second plurality of additional vias is disposed along a second side of the second terminal opposite the first side of the second terminal,
wherein the first plurality and the second plurality of additional vias extend through the substrate from the first side to the second side.
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The instant application relates to DC-DC converters, and more particularly to current distribution in DC-DC converters.
DC-DC converters include active and passive components, including power stage components such as high-side and low-side power transistors, for regulating the voltage of a load such as a processor. Each high-side/low-side power transistor pair forms an output phase of the DC-DC converter which is coupled to the load through a corresponding output inductor. The components of a DC-DC converter, including the power stage components and the output inductors, are attached to a printed circuit board (PCB) together with the load. The PCB has various electrical pathways for electrically interconnecting the DC-DC converter components, including electrically connecting the power stage transistors of the converter to the load. Significant waste heat is expelled by the power stage components and output inductors during operation. Transfer of this heat energy from each power stage and output inductor to the PCB is a critical design consideration.
According to an embodiment of a DC-DC converter, the DC-DC converter comprises a substrate having opposing first and second sides, a power stage attached to the first side of the substrate and comprising active semiconductor components operable to provide an output phase of the DC-DC converter, an inductor attached to the first side of the substrate and electrically connected to the power stage through a first metal trace at the first side of the substrate, and a plurality of electrically conductive vias extending through the substrate from the first side to the second side. The vias are electrically connected to the first metal trace. At least some of the vias are disposed at least partly under the power stage.
According to an embodiment of a method of assembling a DC-DC converter, the method comprises: providing a substrate having opposing first and second sides and a plurality of electrically conductive vias extending through the substrate from the first side to the second side; attaching a power stage to the first side of the substrate so that at least some of the vias are disposed at least partly under the power stage, the power stage comprising active semiconductor components operable to provide an output phase of the DC-DC converter; attaching an inductor to the first side of the substrate so that the inductor is electrically connected to the power stage through a first metal trace at the first side of the substrate; and electrically connecting the first metal trace to the second side through the electrically conductive vias.
Those skilled in the art will recognize additional features and advantages upon reading the following detailed description, and upon viewing the accompanying drawings.
The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts. The features of the various illustrated embodiments can be combined unless they exclude each other. Embodiments are depicted in the drawings and are detailed in the description which follows.
According to embodiments described herein, a DC-DC converter includes at least one power stage having a high-side power transistor and a low-side power transistor. The power transistors can be integrated in the same semiconductor die or in different dies. In either case, each high-side power transistor switchably connects the load to an input voltage of the DC-DC converter, and the corresponding low-side power transistor switchably connects the load to ground at different periods. Each power stage die can be a bare die i.e. an unpackaged die or a packaged die such as a molded die package or an open cavity die package, and each pair of high-side and low-side power stage transistors forms an output phase of the DC-DC converter. Each output phase is coupled to the load by a respective inductor. In the case of a single pair of high-side and low-side power stage transistors, the DC-DC converter is a single-phase converter. In the case of two or more pairs of high-side and low-side power stage transistors, the DC-DC converter is a multi-phase converter.
In either the single-phase or multi-phase case, each power stage die and corresponding output inductor are attached to a substrate such as a PCB. Vias extend through the substrate from one side of the substrate to the other side. Metal traces are provided on the side of the substrate to which the power stage(s) and inductor(s) are attached. The metal traces are spaced apart and electrically isolated from one another, and provide input, output, ground and switched voltage connection points on the substrate for the power stage components.
Some of the vias are electrically connected to the switched voltage trace i.e. the metal trace to which the output of a power stage and a terminal of the corresponding inductor are attached. These vias extend through the substrate to a corresponding metal trace at the opposite side of the substrate. At least some of the vias electrically connected to the switched voltage trace are disposed at least partly under the power stage so as to enhance the transfer of heat energy from that power stage to the backside of the substrate. The switched voltage trace can be replicated in one or more intermediary layers of the PCB and electrically connected to the same group of vias as the switched voltage trace at the front side of the substrate, to reduce the resistance of this electrical pathway.
Each power stage is to be attached to the front side 102 of the substrate 100 and comprises active semiconductor components operable to provide an output phase of the DC-DC converter. The DC-DC converter has more than one phase as shown. In general, the DC-DC converter can be a single-phase or a multi-phase converter as explained above. For example, the section of the substrate 100 shown in
The power stage components of the DC-DC converter include input capacitors, output capacitors, a power stage for each phase of the DC-DC converter and which includes a pair of high-side and low-side power transistors, and an inductor for electrically connecting the corresponding power stage to the load regulated by the DC-DC converter. Each pair of high-side and low-side transistors can be integrated in the same semiconductor die or disposed in separate dies to form one output phase of the DC-DC converter, which is electrically connected to the load by an inductor. A corresponding circuit schematic of one phase formed by a high-side transistor Q1, a low-side transistor, and an inductor 108 is shown in
The front side 102 of the substrate 100 includes various metal traces such as copper traces for electrically connecting the power stage components. The metal traces are separated from one another to prevent shorting. For each phase of the DC-DC converter, the metal traces include an input voltage trace 110 which is at the input voltage potential (VIN) of the DC-DC converter, an output voltage trace 112/114 which is at the regulated output voltage potential (Vout) of the DC-DC converter, one or more ground traces 116 which are at ground potential, and a switched voltage trace 118 electrically connected to the switched voltage output of a power stage. The front side 102 of the substrate 100 also includes various attach regions or pads 120 for attaching different power stage components of the DC-DC converter to the front side 102 of the substrate 100. In the case of a PCB, the front side 102 of the substrate 100 corresponds to the top outer layer of the PCB.
Input capacitors of each phase are connected between the input voltage trace 110 and a ground trace 116 at the front side 102 of the substrate 100. Output capacitors of each phase are connected between the output voltage trace 112 and a ground trace 116. The input node of high-side power transistor Q1 of each phase is connected to the input voltage trace 110, so that the high-side power transistor Q1 can switchably connect the load to the input voltage VIN of the DC-DC converter. The input node of low-side power transistor Q2 of each phase is connected to one of the ground traces 116, so that the low-side power transistor Q2 can switchably connect the load to ground at different periods than when the high-side power transistor Q1 is active. The output node of both power transistors Q1, Q2 is connected to the switched voltage trace 118. One terminal of the inductor is attached to the switched voltage trace 118 and the other terminal of the inductor is attached to the output voltage trace 112, so that the output node of the power transistors Q1, Q2 is electrically connected to the output voltage trace 112 on the substrate through the inductor. A plurality of vias extend through the substrate 100 from the front side 100 to the back side 122 for providing electrical and thermal pathways through the substrate 100.
The back side 122 of the substrate 100 also has various attach regions or pads 132 for attaching different power stage components of the DC-DC converter to the back side 122 of the substrate 100. In the case of a PCB, the back side 122 of the substrate 100 corresponds to the bottom outer layer of the PCB. The footprint of the power stages which are to be attached to the front side of the substrate 100 are illustrated with dashed boxes 104 in
A first group of vias 134 electrically connect the input voltage trace 110 at the front side 102 of the substrate 100 to the corresponding input voltage metal trace 124 at the back side 122 of the substrate 100. A second group of vias 136 electrically connect the output voltage trace 112 at the front side 102 of the substrate 100 to the corresponding output voltage metal trace 126 at the back side 122 of the substrate 100. A third group of vias 138 electrically connect the ground trace(s) 116 at the front side 102 of the substrate 100 to the corresponding ground metal trace(s) 128 at the back side 122 of the substrate 100. A fourth group of vias 140 electrically connect the switched voltage trace 118 at the front side 102 of the substrate 100 to the corresponding switched voltage trace 130 at the back side 122 of the substrate 100. At least some of the vias 140 in the fourth group are disposed at least partly under the power stage as indicated by the power stage footprints 104 shown in
An additional switched voltage trace 146 can be formed in one or more of the intermediary layers 144 as shown in
The circuit board is shown with two intermediary layers 202, 204 interposed between the top and bottom outer layers 200, 206. In general, the circuit board can include more or less than two intermediary layers. In each case, at least one of the intermediary layers 202 can have an additional switched voltage trace 226 which is electrically connected to the same vias 228 as the switched voltage traces 214, 224 at the top and bottom outer layers 200, 206 of the circuit board. The intermediary layer 202 with the additional switched voltage trace 226 can be directly adjacent the top outer layer 200 of the circuit board. The other intermediary layer 204 can be directly adjacent the bottom outer layer 206 and can have a monolithic ground plane 230 through which the vias 228 extend and from which the vias 228 are electrically insulated. Alternatively, the order of the intermediary layers 202, 204 can be reversed so that the layer 202 with the additional switched voltage trace 226 is directly adjacent the bottom outer layer 206 and the intermediary layer 204 with the monolithic ground plane 230 is directly adjacent the top outer layer 200. In some cases, each intermediary layer 202 having an additional switched voltage trace 226 is interposed between adjacent layers 204 having a ground plane 230 for improved noise isolation. In each case, the vias 232 electrically connected to the input voltage traces 208, 218, the vias 234 electrically connected to the output voltage traces 210, 220 and the vias 228 electrically connected to the switched voltage traces 214, 224, 226 are electrically insulated from each intermediary ground plane 230. The vias 236 electrically connected to the ground traces 212, 222 at the top and bottom outer layers 200, 206 are also electrically connected to each intermediary ground plane 230. In general, the circuit board can include one or more intermediary layers having an additional switched voltage trace 226 which is electrically connected to the same vias 228 as the switched voltage traces 214, 224 at the outer layers 200, 206 of the circuit board and which is interposed between an intermediary ground plane 230 and the top or bottom outer layer 200/206. The switched voltage traces 214, 224, 226 disposed in the different layers of the circuit board can be vertically aligned with each other and have the same shape.
A first group 320 of the vias 314 electrically connected to the switched voltage traces 308 is disposed along a first side of the first terminal 306 of each inductor 302. A second group 322 of the vias 314 electrically connected to the switched voltage traces 308 is disposed along a second side of the first terminal 306 of each inductor 302 opposite the first side of the first terminal 306. In one embodiment, the group 320 of vias 314 disposed along the first side of the first terminal 306 of each inductor 302 is aligned along a first center line 324. The group 322 of vias 314 disposed along the second (opposite) side of the first terminal 306 of each inductor 302 is aligned along a second center line 326 which runs parallel with the first center line 324.
A first plurality of additional vias 328 is disposed along a first side of the second terminal 310 of each inductor 302, and a second plurality of additional vias 330 is disposed along a second side of the second terminal 310 of each inductor 302 opposite the first side of the second terminal 310. The additional vias 328, 330 extend through the circuit board and are electrically connected to the output voltage metal traces 312 at both sides (the bottom side of the circuit board is shown in
In an embodiment, a part 332 (also known as inductor footprint or footprint landing pattern) of the circuit board covered by the first terminal 310 of each inductor 302 is devoid of the vias 328, 330. Such a configuration provides for an open current channel 412 in each ground reference plane under the inductors 302 as shown in
Each power stage of the DC-DC converters previously described herein can be attached to a substrate using any standard die attach processes such as soldering, sintering, etc.
Spatially relative terms such as “under”, “below”, “lower”, “over”, “upper” and the like, are used for ease of description to explain the positioning of one element relative to a second element. These terms are intended to encompass different orientations of the device in addition to different orientations than those depicted in the figures. Further, terms such as “first”, “second”, and the like, are also used to describe various elements, regions, sections, etc. and are also not intended to be limiting. Like terms refer to like elements throughout the description.
As used herein, the terms “having”, “containing”, “including”, “comprising” and the like are open-ended terms that indicate the presence of stated elements or features, but do not preclude additional elements or features. The articles “a”, “an” and “the” are intended to include the plural as well as the singular, unless the context clearly indicates otherwise.
With the above range of variations and applications in mind, it should be understood that the present invention is not limited by the foregoing description, nor is it limited by the accompanying drawings. Instead, the present invention is limited only by the following claims and their legal equivalents.
Tang, Benjamim, Todorov, Emil, Sakai, Allen, Kawaguchi, Scott
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